Doomed Flight 3407 was on autopilot until the final 26 seconds before it crashed into a suburban Buffalo home, killing 50 people, a an investigator said yesterday.

The National Transportation Safety Board was bombarded with questions about why the pilot, Capt. Marvin Renslow, did not disengage the autopilot earlier.

During the last horrifying seconds before impact, the turboprop plunged from 1,150 feet to 350 feet above the ground in just five seconds – a plummet that doubled the g-force on the plane and its passengers, said Steve Chealander of the NTSB.

All the while, the plane was making wild movements, pitching up and down like a roller coaster and rolling right and left before falling belly first on a home, killing all 49 people on board and a man in the house.

The plane’s nose was found pointing in the opposite direction of the Buffalo airport, where the pilot of the Continental commuter flight from Newark had been trying to land.

The NTSB is also trying to determine whether the fiery crash was caused by icing.

According to flight recordings, the crew members had reported “significant” icing on the windshield and wings, Chealander said.

But they didn’t mention the degree of icing – light, moderate or severe. The airline’s regulations require pilots to fly manually through “severe” icing.

Chealander said his agency believes pilots should avoid autopilots under any icing conditions, “to better feel the airplane.”

The NTSB has been urging the Federal Aviation Administration to enact stricter regulations regarding the use of autopilot in hazardous conditions.

“They see things a little differently,” Chealander said. “We can only make the recommendation. We don’t have regulatory power.”

Laura Brown, a spokeswoman for the FAA, said, “We have a general guidance that pilots should take autopilot off in icing conditions unless the aircraft is certificated for autopilot in those conditions.

“If the plane is certificated to operate autopilot in icing conditions, you can better maintain control of the plane.”

She did not say whether the Continental plane, which was operated by Colgan Airlines, was certified for autopilot flight in ice.

Chealander said it’s believed that the icing condition on the wings was between light and medium. Eleven minutes into the flight, the crew activated the de-icing system, which uses pneumatic tubes to break up ice.

It appears Capt. Renslow, who had 3,379 hours of flight time, did not disengage the autopilot until the cockpit “stick shaker,” which warns a pilot if a stall is imminent, activated. By then, there were just seconds left before the plane’s deadly descent.

Meanwhile, 15 bodies have been removed from the crash site, but workers may need another four days to recover the rest, and a snowstorm is approaching.

Three more victims were identified: George Abu Karam, from Tiberias, Israel; Jerome Krasuski, 53 of suburban Buffalo; and Sean Lang, 19, of Montgomeryville, Pa.

Karam was a former member of the South Lebanon army, en route to Buffalo to visit a cousin.